program exited non-zero, C<$!> will be set to C<0>.) Closing a pipe
also waits for the process executing on the pipe to complete, in case you
want to look at the output of the pipe afterwards, and
-implicitly puts the exit status value of that command into C<$?>.
+implicitly puts the exit status value of that command into C<$?> and
+C<${^CHILD_ERROR_NATIVE}>.
Prematurely closing the read end of a pipe (i.e. before the process
writing to it at the other end has closed it) will result in a
instead a Perl builtin. To get somewhat similar but locale dependent date
strings, see the example in L</localtime>.
+See L<perlport/gmtime> for portability concerns.
+
=item goto LABEL
=item goto EXPR
Note that the C<%a> and C<%b>, the short forms of the day of the week
and the month of the year, may not necessarily be three characters wide.
+See L<perlport/localtime> for portability concerns.
+
=item lock THING
This function places an advisory lock on a shared variable, or referenced
=item mkdir FILENAME
+=item mkdir
+
Creates the directory specified by FILENAME, with permissions
specified by MASK (as modified by C<umask>). If it succeeds it
returns true, otherwise it returns false and sets C<$!> (errno).
-If omitted, MASK defaults to 0777.
+If omitted, MASK defaults to 0777. If omitted, FILENAME defaults
+to C<$_>.
In general, it is better to create directories with permissive MASK,
and let the user modify that with their C<umask>, than it is to supply
}
}
-See L<perliol/> for detailed info on PerlIO.
+See L<perliol> for detailed info on PerlIO.
You may also, in the Bourne shell tradition, specify an EXPR beginning
with C<< '>&' >>, in which case the rest of the string is interpreted
of $^F. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
-child to finish, and returns the status value in C<$?>.
+child to finish, and returns the status value in C<$?> and
+C<${^CHILD_ERROR_NATIVE}>.
The filename passed to 2-argument (or 1-argument) form of open() will
have leading and trailing whitespace deleted, and the normal
U A Unicode character number. Encodes to UTF-8 internally
(or UTF-EBCDIC in EBCDIC platforms).
- w A BER compressed integer. Its bytes represent an unsigned
- integer in base 128, most significant digit first, with as
- few digits as possible. Bit eight (the high bit) is set
- on each byte except the last.
+ w A BER compressed integer (not an ASN.1 BER, see perlpacktut for
+ details). Its bytes represent an unsigned integer in base 128,
+ most significant digit first, with as few digits as possible. Bit
+ eight (the high bit) is set on each byte except the last.
x A null byte.
X Back up a byte.
- @ Null fill to absolute position, counted from the start of
- the innermost ()-group.
+ @ Null fill or truncate to absolute position, counted from the
+ start of the innermost ()-group.
+ . Null fill or truncate to absolute position specified by value.
( Start of a ()-group.
Some letters in the TEMPLATE may optionally be followed by one or
nNvV Treat integers as signed instead of unsigned.
+ @. Specify position as byte offset in the internal
+ representation of the packed string. Efficient but
+ dangerous.
+
> sSiIlLqQ Force big-endian byte-order on the type.
jJfFdDpP (The "big end" touches the construct.)
Each letter may optionally be followed by a number giving a repeat
count. With all types except C<a>, C<A>, C<Z>, C<b>, C<B>, C<h>,
-C<H>, C<@>, C<x>, C<X> and C<P> the pack function will gobble up that
-many values from the LIST. A C<*> for the repeat count means to use
-however many items are left, except for C<@>, C<x>, C<X>, where it is
-equivalent to C<0>, and C<u>, where it is equivalent to 1 (or 45, what
-is the same). A numeric repeat count may optionally be enclosed in
-brackets, as in C<pack 'C[80]', @arr>.
+C<H>, C<@>, C<.>, C<x>, C<X> and C<P> the pack function will gobble up
+that many values from the LIST. A C<*> for the repeat count means to
+use however many items are left, except for C<@>, C<x>, C<X>, where it
+is equivalent to C<0>, for <.> where it means relative to string start
+and C<u>, where it is equivalent to 1 (or 45, which is the same).
+A numeric repeat count may optionally be enclosed in brackets, as in
+C<pack 'C[80]', @arr>.
One can replace the numeric repeat count by a template enclosed in brackets;
then the packed length of this template in bytes is used as a count.
byte (so the packed result will be one longer than the byte C<length>
of the item).
+When used with C<@>, the repeat count represents an offset from the start
+of the innermost () group.
+
+When used with C<.>, the repeat count is used to determine the starting
+position from where the value offset is calculated. If the repeat count
+is 0, it's relative to the current position. If the repeat count is C<*>,
+the offset is relative to the start of the packed string. And if its an
+integer C<n> the offset is relative to the start of the n-th innermost
+() group (or the start of the string if C<n> is bigger then the group
+level).
+
The repeat count for C<u> is interpreted as the maximal number of bytes
to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
count should not be more than 65.
is the string "\0a\0\0bc".
-
=item *
C<x> and C<X> accept C<!> modifier. In this case they act as
$bar = pack('s@4l', 12, 34);
# short 12, zero fill to position 4, long 34
# $foo eq $bar
+ $baz = pack('s.l', 12, 4, 34);
+ # short 12, zero fill to position 4, long 34
$foo = pack('nN', 42, 4711);
# pack big-endian 16- and 32-bit unsigned integers
behind the scenes. Before C<require> looks for a "F<.pm>" extension,
it will first look for a filename with a "F<.pmc>" extension. A file
with this extension is assumed to be Perl bytecode generated by
-L<B::Bytecode|B::Bytecode>. If this file is found, and it's modification
+L<B::Bytecode|B::Bytecode>. If this file is found, and its modification
time is newer than a coinciding "F<.pm>" non-compiled file, it will be
loaded in place of that non-compiled file ending in a "F<.pm>" extension.
is implementation-dependent. See also L<perlport> for notes on the
portability of C<select>.
+On error, C<select> returns C<undef> and sets C<$!>.
+
+Note: on some Unixes, the select(2) system call may report a socket file
+descriptor as "ready for reading", when actually no data is available,
+thus a subsequent read blocks. It can be avoided using always the
+O_NONBLOCK flag on the socket. See select(2) and fcntl(2) for further
+details.
+
B<WARNING>: One should not attempt to mix buffered I/O (like C<read>
or <FH>) with C<select>, except as permitted by POSIX, and even
then only on POSIX systems. You have to use C<sysread> instead.
produces the output 'h:i:t:h:e:r:e'.
-Using the empty pattern C<//> specifically matches the null string, and is
-not be confused with the use of C<//> to mean "the last successful pattern
-match".
+As a special case for C<split>, using the empty pattern C<//> specifically
+matches only the null string, and is not be confused with the regular use
+of C<//> to mean "the last successful pattern match". So, for C<split>,
+the following:
-Empty leading (or trailing) fields are produced when there are positive width
-matches at the beginning (or end) of the string; a zero-width match at the
-beginning (or end) of the string does not produce an empty field. For
-example:
+ print join(':', split(//, 'hi there'));
+
+produces the output 'h:i: :t:h:e:r:e'.
+
+Empty leading (or trailing) fields are produced when there are positive
+width matches at the beginning (or end) of the string; a zero-width match
+at the beginning (or end) of the string does not produce an empty field.
+For example:
print join(':', split(/(?=\w)/, 'hi there!'));
printf "child exited with value %d\n", $? >> 8;
}
-or more portably by using the W*() calls of the POSIX extension;
-see L<perlport> for more information.
+Alternatively you might inspect the value of C<${^CHILD_ERROR_NATIVE}>
+with the W*() calls of the POSIX extension.
When the arguments get executed via the system shell, results
and return codes will be subject to its quirks and capabilities.
Behaves like the wait(2) system call on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
-C<-1> if there are no child processes. The status is returned in C<$?>.
+C<-1> if there are no child processes. The status is returned in C<$?>
+and C<{^CHILD_ERROR_NATIVE}>.
Note that a return value of C<-1> could mean that child processes are
being automatically reaped, as described in L<perlipc>.
Waits for a particular child process to terminate and returns the pid of
the deceased process, or C<-1> if there is no such child process. On some
systems, a value of 0 indicates that there are processes still running.
-The status is returned in C<$?>. If you say
+The status is returned in C<$?> and C<{^CHILD_ERROR_NATIVE}>. If you say
use POSIX ":sys_wait_h";
#...